Isolation and Characterization of Circulating Tumor Cells in a Highly Metastatic Model of Pancreatic Neuroendocrine Tumors

Circulating tumor cells (CTCs) shed into the bloodstream from primary tumors are essential mediators of the hematogenous spread of primary lesions to distant organs. Isolation and molecular characterization of CTCs provide a powerful tool to better understand the metastatic cascade and identify putative drivers of metastases.

Here, we use a mouse model of pancreatic neuroendocrine tumors, RIP-Tag2, which is highly metastatic when inbred in a specific mouse strain, showing invasive beta cell carcinomas and hundred percent of micrometastases penetrance, showing evidence of hematogenous dissemination. We describe the isolation of circulating tumor cells using Leucine-rich repeat-containing G-protein coupled receptor 5 (Lgr5) as a new biomarker for tumor beta cells in this model. Lgr5 is a well–established marker of adult stem cells. Here, we observed a broad expression of Lgr5 into the tumor tissue, not only confined to a restrictive compartment of cells. Indeed, we identify an extensive expression of Lgr5 at cytoplasmic and membranous level, in primary tumor cells, metastases and neoplastic emboli, making Lgr5 a good candidate as a biomarker for tumorigenic beta cells, including CTCs. After successful isolation and first characterization of the cells, the second step of this study consists of transcriptome single cell analyses of these CTCs, together with the genetic profiling of matched laser captured liver metastases. This strategy should lead to identification of circulating tumor cells heterogeneity as well as putative actors of extravasation and metastatic colonization in pancreatic neuroendocrine tumors.